We are continuing to pursue our goals of characterizing nuclear RNA's and nuclear proteins engaged in interactions between nucleus and cytoplasm and which appear to be engaged in the regulation of gene expression or replication or both. Basic characterizations of those kinds of molecules under different circumstances are achieved in amebas by transplanting appropriately labeled nuclei between cells and assaying by autoradiography of electrophoretic gels the kinds of molecules present in nucleus and cytoplasm and the kinds of molecules that move between the two compartments. We also are characterizing how the behavior of these molecules may vary under different conditions. To assess the roles of similar moleucles in cell function we are following their fate in cells, such as Friend's erythroleukemic cells, that can be manipulated in vitro to markedly change their gene expression and in cells, such as Tetrahymena, in which two nuclei performing markedly different functions are present in a common cytoplasm. We are finding that as activities change, so does the intranuclear pattern of these molecules and we are attempting to draw meaningful generalizations about their roles in cell function from our observations.